This invention relates to oscillator circuits, and more particularly, to a very high frequency oscillator circuit exhibiting improved stability.
The highest frequency of oscillation of a semiconductor oscillator is theoretically limited only by the characteristics of the semiconductor device that is used in the oscillator circuit. However, in practice, many other constraints apply. One such constraint is the inability to physically construct a circuit that can meet the circuit constants needed to support the desired frequency of oscillation. In many cases, it is impractical to fabricate the main inductive frequency determining element to a low enough value to satisfy the resonant frequency equations. Another problem concerns itself with minimizing the series inductance of the various capacitive and other circuit elements. If these unavoidable parasitic inductive elements are not small enough compared to the main frequency determining inductance, then unstable or unpredictable operation results.
Another problem with high frequency oscillator operation is that circuit capacitances must be reduced as the operating frequency is increased. The limiting case is usually when all capacitances are eliminated until only the semiconductor internal capacitances and the unavoidable stray capacitances remain. Under these conditions, the circuit is unstable with changes in temperature or/and supply voltage as no temperature compensating elements are present. It is improbable that device to circuit match or that feedback would be optimum.
It would be desirable then to have a high frequency oscillator circuit having a high enough frequency determining inductance to allow repeatable fabrication. It would further be desirable to have very high frequency oscillator characterized by a high ratio of main inductance to parasitic circuit inductance. It would also be desirable to have a very high frequency oscillator which enables compensation for temperature changes in circuit operation, and which is characterized by the capability of adjusting circuit feedback and circuit match to both the input and output ports of the active element of the oscillator circuit.